This invention relates generally to the generation and use of high energy electron beams and is particularly directed to an electron device incorporating an electron beam deflection lens for use in electron beam lithography.
In general, semiconductor devices are manufactured using photolithography techniques for reproducing the image of a reticle onto a photosensitive resist-covered semiconductor wafer. A light source in this photolithography approach typically directs ultraviolet (UV) light onto the photosensitive resist-covered semiconductor wafer. As the line width becomes more and more narrow such as in forming more compact electronic circuits, i.e., line widths of 0.35 xcexcm and below, a UV light source of shorter wavelength is required. As the UV wavelength decreases, an optical glass lens becomes opaque to the UV light and a quartz optical lens is required. Even through quartz, transmission of UV light is limited resulting in corresponding limits on the intensity of the UV light directed onto the substrate. The use of quartz also increases the cost of this approach. In addition, with shorter wavelength UV light, the depth of focus also becomes proportionately more critical. Thus, the semiconductor wafer""s surface flatness requirement becomes increasingly more difficult and costly to achieve.
Another approach has also been adopted in the fabrication of semiconductor devices. This latter approach employs an electron beam directed onto the semiconductor wafer for tracing out the desired integrated circuit pattern. This electron beam lithography approach also suffers from limitations which have restricted its adoption on a widespread basis in the fabrication of semiconductor devices. For example, the speed available in tracing the electron beam over the semiconductor wafer (substrate) is much slower than the speed achievable in a standard step-and-repeat optical device used in the above-described photolithography manufacturing approach. Also, current electron beam sources for use in semiconductor device lithography are too expensive and bulky to permit their adoption on a wide scale in the manufacture of semiconductor devices.
The present invention addresses the aforementioned limitations of the prior art by providing an electron beam device for use in electron beam lithography in the fabrication of semiconductor integrated circuits which does not require an expensive optical light source and lens mask combination, is capable of forming line widths of extremely small size on a semiconductor wafer, possesses a depth of focus at least ten times greater than that available in optical systems, employs a multi-stage digitized beam deflection system which provides precise control of electron beam position, and is compact in shape, small in size and of low cost.
Accordingly, it is an object of the present invention to provide apparatus for electron beam lithography such as used in the manufacture of semiconductor integrated circuit devices.
It is another object of the present invention to provide a small, compact electron beam device which can be used in two- and three-dimensional matrix arrays for producing dense circuit designs in simultaneously fabricating large numbers of semiconductor integrated circuit devices.
Yet another object of the present invention is to provide an electron beam device capable of directing an electron beam of very small cross section onto a substrate and precisely controlling the position of the beam on the substrate for fabricating a micro-miniature semiconductor integrated circuit device.
A further object of the present invention is to provide an electron beam source having a large depth of focus which is capable of accommodating substrates having reduced flatness characteristics in the manufacture of semiconductor integrated circuit devices by means of electron beam lithography.
This invention contemplates an electron beam device incorporating a beam deflection lens for the simultaneous deflection and focusing of the electron beam on a target surface such as a substrate used in the manufacture of semiconductor integrated circuit devices. The electron beam device further includes a beam source for directing an electron beam through plural aligned apertured plates arranged in a spaced manner along the direction of travel of the beam. Each of the plates includes a respective limiting aperture aligned along the beam axis, with the limiting apertures decreasing in diameter in proceeding along the direction of travel of beam. The apertured plates intercept peripheral portions of the electron beam in reducing beam cross section to provide a very narrow, precisely defined electron beam incident upon the substrate. Positioning electrodes may also be concentrically disposed about the beam axis and disposed between adjacent apertured plates for centering the beam. The beam limiting arrangement may also be in the form of a single apertured plate with a tapered aperture which is larger on the surface of the plate in facing relation to the source of energetic electrons. After transiting the beam limiting apertures in the aligned plates, the beam is then directed through a cylindrical shaped focusing electrode and then passes through plural electrostatic charged deflection plates disposed in a spaced manner about the electron beam. The position of incidence of the electron beam on the substrate is precisely controlled by the electrostatic charges applied to the deflection plates. The deflection plates are angled away from the beam axis in proceeding along the direction of travel of the beam to provide precise, highly sensitive control of electron beam positioning. After transiting the deflection plate stage, the electron beam is further focused by means of a second electrostatic lens which also may be in the form of plural, flat, charged plates disposed in a spaced manner about the beam. Alternatively, the second electrostatic lens may also be a single member cylindrical in shape. The electron beam is simultaneously focused and deflected by means of the unique deflection lens arrangement of the inventive electron beam device for providing a small, compact device which can be arranged in two- and three-dimensional matrix arrays for simultaneously fabricating large numbers of dense electronic circuits in plural semiconductor integrated circuit devices. The electron beam is of a very small cross section and may be displaced, i.e., deflected over the substrate, for high speed, high density semiconductor integrated circuit device fabrication.